The objective of the proposed research is to quantitate the influences of factors which may modify susceptibility to oxygen toxicity in patients with pulmonary insufficiency. Effects and interactions which will be studied include those of acute and chronic hypercapnia and chronic hypoxia with and without chronic hypercapnia. Survival times in large numbers of rats will be used to study these effects at oxygen pressures of 1.0, 1.5, 2.0, 3.0 and 4.0 ata. Over this range of oxygen pressures we will study effects on pulmonary oxygen poisoning, with an increasing degree of neuroendocrine interaction in the absence of convulsions at the lower pressures and in their presence at higher pressures. Analysis and description of the effects will be aided by an experimental design which facilitates employment of previously used probability-log transformations of data to define susceptibility to oxygen toxicity at a single pressure and log-log transformations to define relative effects at different oxygen pressures. Analysis and description of the mortality data will be complemented by studies designed to identify biochemical correlates of the observed changes in susceptibility to neurologic and pulmonary oxygen poisoning.